ASoC: hdmi-codec: remove reference to the dai drivers in the private data

Keeping the a pointer to the dai drivers is not necessary. It is not used
by the hdmi_codec after the probe.

Even if it was used, the 'struct snd_soc_dai_driver' can accessed through
the 'struct snd_soc_dai' so keeping the pointer in the private data
structure is not useful.

Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Mark Brown <broonie@kernel.org>